Microcapsules are employed to a large extent in the perfumery and flavoring industries. They constitute delivery systems for perfuming or flavoring ingredients and can be advantageously used in a very large number of applications. The encapsulation of active substances such as perfuming or flavoring ingredients provides at the same time a protection of the ingredients there-encapsulated against “aggressions” such as oxidation or moisture and allows, on the other hand, a certain control of the kinetics of flavor or fragrance release to induce sensory effects through sequential release.
Now, the numerous advantageous properties of microcapsules in these fields are opposed to other properties that must be taken into account during their preparation, transportation, storage and handling. In fact, such delivery systems, due to their nature, and in particular to the fact that they encapsulate volatile and flammable substances, constitute combustible dusts which can, when dispersed in air or another oxygen-containing gas, form readily ignitable mixtures. When ignited by a sufficient powerful ignition source, the result is a rapid combustion reaction with advancing pressure and flame front.
This issue becomes important during the preparation of microcapsules. In particular, spray-drying and fluidized-bed encapsulation processes are highly concerned by this issue, as they are both based on the use of an equipment wherein particles are suspended in hot air as fine particles and can therefore undergo explosion during their preparation.
Spray-drying is the most common encapsulation technique used to stabilize volatile substances such as flavors or fragrances, by encapsulating them in a solid form, suited to many applications. Spray-dried powders are commonly made in an usual spray-drying equipment. Spray-drying is usually effected by means of a rotating disc or of multi-component nozzles. Detailed techniques are described for instance in K. Masters, Spray-drying Handbook, Longman Scientific and Technical, 1991.
Fluidized beds are used for spraying a coating on a core material fluidized in a bed, or agglomerating and/or granulating powders. This encapsulation technique is also well known and is described for instance in EP 70719 or in U.S. Pat. No. 6,056,949, the contents of each of which are expressly included herein by reference thereto.
Both the above-described encapsulation equipments being susceptible to explosions of particles suspended in the air, they thus have to be adapted as a function of the technical safety parameters characterizing the particles there-treated. In particular, they have to be dimensioned as a function of the violence of explosions that can occur during the preparation of microcapsules. Therefore, the problem of reducing the violence of possible explosions of powder products resulting from such encapsulation processes is of paramount importance for the industry.
For the safe handling of combustible substances, it is imperative to know the dangerous properties of a product. The reliable way to characterize the combustible and explosive properties of a product is to subject a sample of the product to various tests and classify the results in accordance with the technical safety characteristics. The international standards (VDI Guideline 2263 part 1: Dust Fires and Dust Explosions, Hazard Assessment-Protective Measures, Test Methods for the Determination of Safety Characteristics of Dusts, Beuth, Berlin, May 1990) describe the test equipments (Modified Hartmann apparatus and Close apparatus, 20-litre sphere apparatus) and methods, namely the ISO standard procedure ISO 6184/1. These methods allow to determine physical constants such as the maximum explosion behavior of a combustible dust in a closed system. A pyrotechnic igniter with a total energy of 10 kJ is used as ignition source. From test methods described in the mentioned guidelines, a characteristic constant, K-St, which is dust specific is determined. As there are so many such dusts produced and processed in industrial practice, for example for pharmaceutical and cereal, flour products, it is appropriate to assign this maximum explosion constant to one of the several dust explosion classes and to use these as a basis for the dimensioning of constructional protective measures. The correspondence between these classes hereafter referred as dust hazard classes, and the constant K-St is the following:
Dust Hazard ClassProduct Specific Constant K-St [bar · m · s−1]St-1 0 to 199St-2200 to 299St-3≧300
Now, although some perfuming and flavoring ingredients are classified in a dust hazard class St-1, a large number of these ingredients and thus the microcapsules encapsulating them, and depending on the volatility of the perfuming or flavoring ingredients, are still classified under an St-2 dust hazard class and thus require production equipments specifically adapted to the violence of possible explosions, which of course can be very costly.
WO 03/043728 A1 (FIRMENICH) discloses perfuming or flavoring microcapsules having fireproofing agents dispersed in or absorbed within a polymeric carrier material, whereby these fireproofing agents were basically inorganic salts.
In view of these fireproofing agents, other agents suitable as explosion suppressants having further beneficial properties are needed. There is in particular a need of finding more efficient fireproofing agents, which can be used with similar efficiency in smaller amounts, and there is a need of fireproofing agents that have a beneficial effect on the hygroscopicity of the perfuming or flavoring microcapsules, notably it would be an advantage to have a fireproofing agent that reduces hygroscopicity of the perfuming or flavoring microcapsules if compared to fireproofing agents of the prior art. In addition, the fireproofing agents disclosed in WO 03/043728 are not always suitable for use in food applications and other solutions have thus to be found.
The present invention now satisfies these needs.